51 characters (including all transformations and shared slots) is still my number. Of course, the way I see it, the "total range" is 45-53, and the "likely range" is 48-52.
Here's why I think we'll get 51 playable characters.
Smash 64 had 12 playable characters.
Melee had 26 playable characters.
Brawl had 39 playable characters.
So, if I did the math right the last 3,587 times (that's a random #, don't worry!),
Melee had 14 more characters than Smash 64, and Brawl had 13 more characters than Melee.
Now, seeing as how there are 2 games being made, we got double the staff. We also have double the games, so there could be all kinds of crazy things. However, I don't see many character cuts, because of how "tight" things will be. Plus, on top of that, the roster is pretty "complete" as it is. Almost every character has been or is close to being "great" to play as in smash bros. Many of the clones have been steadily decloned (even though that isn't actually a word).
And on top of that, to prove my point I doubt we'll see many, if any cut characters, Sakurai and co. will likely transfer the playable character data from Brawl to Smash WiiU and 3DS. That means they won't make ALL the characters all over again like they did in Brawl. Instead, we will get some transfers, like what happened with Smash 64. This is literally easier than adding clones. All the staff at Namco Bandai has to do is update their models, maybe give the characters a few new animations, give a select few characters a new move or two, balance them with the rest of roster, and then then test them out. That's it.
With that in mind, they'll likely re-add Mewtwo (who could have some data transferred he has in Melee and Brawl) and possibly even Roy (although that is doubtful). Then, from there, I imagine 10-13 new characters will be built from scratch. Seeing as how Sakurai is content with taking his sweet time (which means a better game for us), and how Nintendo is fine with that, and willing to fund these 2 projects in the long run, I see this roster prediction being true.
However, that doesn't account for DLC characters. If there's 1 or 2 characters that couldn't make it into the final game, but are in DLC, fine. That's foreseeable, albeit not all that likely. But if there are any more DLC "incomplete" characters than that, or newly crafted DLC characters that weren't previously planned, and all debts are off. Although, to be quite honest, I would be all for that, wallet and all.
Edit: Also, 100th post on this thread! YESSSS!!!